PALEOSOLS AND STRATIGRAPHY OF THE SCENIC-POLESLIDE MEMBER BOUNDARY: IMPLICATIONS FOR PEDOFACIES ANALYSIS AND REGIONAL CORRELATION OF THE EARLY OLIGOCENE BRULE FORMATION, SOUTH DAKOTA, USA

A pedostratigraphy was devised for paleosols that formed at approximately 31.2 Ma along the Scenic-Poleslide Member boundary and a temporally equivalent zone within the Oligocene Brule Formation of the White River Group in Badlands National Park, South Dakota. Three formal pedostratigraphic units were defined: the Kudrna 1 Paleosol, Sheep 1 Paleosol, and Castle 1 Paleosol, with type and reference sections. The Kudrna 1 Type Paleosol is a moderately developed paleosol with a zone of subsoil clay accumulation overlying a pedogenic carbonate horizon. The Sheep 1 Paleosol formed in a temporally equivalent zone to the Kudrna 1 and is a moderately developed paleosol with cambic subsoil features and pedogenic carbonate throughout. The Castle 1 Paleosol, which overlies the Kudrna 1, is a weakly developed soil formed in volcaniclastic fallout, with little to no evidence of weathering and clay accumulation. All paleosols show some degree of overprinting and/or soil welding. The degree of smectite alteration, soil welding, leaching, and clay accumulation, decreases towards the southwest. These differences are explained using an eolian and fluvial pedofacies model and are comparable to a modern day soil transect along the Platte River, Nebraska. The pedostratigraphic results of the Kudrna 1 and Sheep 1 Paleosols allow a more in-depth paleoenvironmental reconstruction of the Scenic-Poleslide Member boundary. The Kudrna 1-Sheep 1 complex provides a baseline pedostratigraphy for future paleosol investigations in the White River Group. In addition to this, the Castle 1 Paleosol contains a volcaniclastic fallout component, formally defined as the Cactus Flat Bentonite (CFB) bed, which can be used in regional correlation with deposits in Nebraska.